Circuit-interrupter releasing apparatus



May 15, 1956 J. WEGENER CIRCUIT-INTERRUPTER RELEASING APPARATUS 2 Sheets-Sheet 1 Filed April 9, 1952 Fig. 2

In ve nzor May 15, 1956 J. WEGENER 2,746,003

CIRCUIT-INTERRUPTER RELEASING APPARATUS Filed April 9, 1952 2 Sheets-Sheet 2 United States Patent 2,746,003 cmouir-mrnnnurran EELEASING APPARATUS Johannes Wegener, therlimfiiemensstadt, Germany, assignor to Siemens Sehuclrertwerlre Alrtiengesellschaft, Berlin-Siemensstadt, Germany, a German corporation Application April 9, 1952, Serial No. 281,421 Claims priority, application Germany May 24, 1951 6 Claims. (Cl. 321-48) My invention relates to electric control apparatus for issuing releasing pulses to a contact device for interrupting an alternating-current circuit and, in one of its specific out not exclusive aspects, to pulse-issuing apparatus for controlling the circuit-opening performance of contact rectifiers.

To secure an arcless circuit interruption, such release control apparatus have been designed to issue a releasing pulse in such a phase relation to the wave of the alternating current to be interrupted that the circuit opening moment occurs at or near the zero passage of the current. For this purpose, a saturable transformer has been used, preferably with an iron core having a sharp bend in its magnetic saturation characteristic. When the primary winding of such a transformer is traversed by the alternating current, its core is saturated most of the time and becomes temporarily unsaturated only near or at the moments of the current zero passages. At those moments, the core becomes reversely magnetized. During the short reversing intervals a current pulse is induced in the secondary winding, and this pulse is applied to the circuit-interrupting contact device for effecting its circuit opening performance. Since the releasing pulse would normally occur shortly after the current zero passage, the saturable transformer is given a premagnetizing excitation which may be produced by means of a current flowing through an additional bias winding. Such a transformer issues the releasing control pulses shortly prior to the current zero passages. However, the interval of time elapsing from the pulse moment at which the secondary transformer current reaches the critical minimum magnitude needed for effecting the release, to the moment when the current to be controlled passes through the zero value is not definitely fixed but is dependent upon the magnitude of the current to be interrupted. This is undesirable and troublesome for applications where large fluctuations in load current are to be expected.

It is therefore an object of my invention to devise pulse-issuing release control apparatus capable of producing pulses prior to the current zero passage at a moment whose phase distance from the zero passage maintains a desired constant value regardless of changes in the magnitude of the current to be controlled; and it is also an object of the invention to achieve this aim by circuit means of utmost simplicity.

Relating to pulse-released circuit interrupters, such as contact converters with series-connected saturable switching reactors, it is another object of my invention to improve the accuracy and reliability of the release control means so as to permit using smaller switching reactors than otherwise necessary.

To attain these objects, and in accordance with a tea ture of my invention, I provide the pulse-issuing saturable transformer, in an organization of the above-mentioned kind, with a premagnetizing excitation proportional to the differential quotient (rate of change) of the alternating current to be interrupted, and also with a superimposed premagnetization of constant magnitude.

If the excitation of the saturable pulse-issuing transformer were made dependent upon the current to be interrupted and upon the rate of change of this current, the starting moment of the pulses produced in the secondary transformer winding would always occur a definite time prior to the zero passage of this current regardless of the current magnitude. However, the pulse would not always reach the critical amplitude required for effecting a release a constant interval ahead of the zero passage of the current to be interrupted, because the pulse magnitude is dependent upon that of the current to be interrupted. Due to the fact, however, that the saturable pulse-issuing transformer is also premagnetized by a constand component of excitation, this dificulty is obviated and the pulses induced in the secondary winding have the critical releasing magnitude always at the same or substantially the same moment prior to the zero passage of the current to be interrupted. When this fixed phase difference is made equal to the inherent time delay period of the switch, the switch will always open the circuit at the current zero passage.

if, as is usually done, a saturable switching reactor is series connected in the load circuit to be controlled, for producing a weak-current interval near the current zero passages, the switching reactor can be of smaller size than otherwise permissible. This is due to the certainty, secured by the invention, of having the releasing pulse always reach the necessary release value within fixed period of time suflicient to have the interrupting performance of the switch safely occur at the current zero passage or within the short weak-current interval.

The foregoing and more specific objects and features of my invention will be apparent from the following description of the embodiments exemplified by the drawing in which:

Fig. 1 is a schematic circuit diagram of a pulse-issuing release control apparatus;

Figs. 2, 3 and 4 are interrelated coordinate diagrams explanatory of the operation of such apparatus;

Fig. 5 shows a schematic circuit diagram of another embodiment of the invention; and

Pi". 6 is the basic circuit diagram of contact rectifier equipped according to Fig. 1.

According to Fig. l the switch 1 for interrupting the circuit of an alternating current i1 has a release control coil 2 which causes the switch 1 to open when coil 2 receives a control pulse from a saturable pulse-issuing transformer 3. Transformer 3 has a primary winding 4 series connected in the circuit to be controlled and hence is excited by the current ii to be interrupted. A second winding 5 on transformer 3 is excited by another current i2. Winding 5 is connected in series with a comparatively large ohmic resistance 8 across an inductance coil 9 in the main circuit to be interrupted. Consequently, the current i2 in winding 5, caused by the counter voltage induced in the inductance coil 9, is dependent upon the differential quotient or rate of change of the current 1']. The transformer 3 is further equipped with a winding 6 which is connected through a large ohmic resistance ll) to a direct current source 11 of constant voltage. The secondary Winding 7 of transformer 3 is connected to the release control winding 2 of switch 1 through a half-Wave rectifier 12. The operation of the release control apparatus Will be explained presently with reference to Figs. 2, 3 and 4.

In the coordinate diagrams shown in Figs. 2 to 4, the ordinate values represent current magnitudes and the abscissas represent time. Fig. 2 shows the time curves of the alternating current ii to be interrupted and a three-phase with release control appanius also the sum ii+iz of the two currents which supply alternating excitation for the saturable pulsing transformer 3. For simplicity, it may be assumed that the magnetizable core of the transformer has a rectangular magnetic characteristic of negligible hysteresis. As apparent from the diagram of Fig. 2, the sum of currents i1+i2 passes through zero at a moment to prior to the zero passage of the current it. Since the impedances of the primary windings 4 and 5 are small compared with the rest of their circuits, the wave shape of the current curves 1 and i2 and i1+i2 will remain substantially sinusoidal. At the moment to, disregarding the direct current excitation of the transformer, a current is (Fig. 3) is induced in, the transformer secondary 7. This current as it increases from zero has at first substantially the same rate of increase or inclination as the current sum ii-l-is. As soon as the reversed magnetization of the transformer core has reached saturation, the secondary current is starts decaying in dependence upon the load of the secondary transformer circuit.

If the magnitude of the current ii in the main circuit changes, the current sum i1+i2 changes accordingly and passes through the zero value with a different steepness. As a result, the shape of the secondary pulses is varies, for instance, as indicated by broken lines in Fig. 3. The horizontal line is. in Fig. 3 denotes the critical value of the release current required for causing the winding 2 to open the switch 1. it will therefore be apparent that the period of time elapsing from the zero moment to to the moment at which the current is reaches the value in, differs depending upon the magnitude of the current ii to be interrupted.

However, since the transformer has also a constant premagnetization, the just-mentioned conditions are greatly improved, especially if the constant premagnetization (or the corresponding constant bias current) is selected to be equal or approximately equal to the critical value is. in the latter case the undesired currentresponsive variation in the timing of the releasing effect is virtually eliminated. In Fig. 2, the constant directcurrent flowing in winding 6 to provide the just-mentioned constant excitation of transformer 3 is indicated by the horizontal line is. This premagnetizing current is equal to the critical releasing current in. As a result, the pulse in winding 7 is no longer produced at the moment to when the current sum ir-l-iz passes through zero but occurs at an earlier moment it namely when the curve of sum i1+iz intersects the line of current is, because now the reverse magnetization of the saturable transformer occurs likewise at the earlier moment it. The resulting current pulses is in the secondary winding '7 are represented in Fig. 4. It will be recognized that even though these pulses assume different wave shapes for respectively different magnitudes of the primary current, they always reach the required current magnitude is. at the same instant; and this instant coincides with the moment to of the zero passage of the current sum i1+i2.. Thus, because the inclination of the current pulse is changes with the inclination of the summation current i1+iz in the vicinity of its passage through zero (as a result of changes in magnitude of the current ii), the interval between the moments t1 and to for various values of the main current i, automatically adjusts itself so that the release current is. is always reached at the instant in when the summation current i1+i2 passes through zero. Consequently, the interval of time from this moment to the zero passage of the primary current to be interrupted remains constant regardless of the magnitude of the primary current. The latter interval is preferably made equal to the time delay period of the switch or, when using a saturable switching reactor, is made somewhat shorter than that time delay period.

While, as mentioned, the constant excitation current of the pulsing transformer is preferably chosen in accordance with the magnitude of the criticalrelease cutrent, slight departures from this magnitude are readily permissible.

The foregoing considerations involve the tacit assumption that all windings on the saturable pulsing transformer have the same number of turns. If this is not the case, then the ampere-turns values of the respective windings are to be used instead of the excitation currents in the foregoing considerations.

In the illustrated example, a valve 12 is series connected with the release control coil 2 of the switch. This valve serves to pass a pulse through switch control coil 2 only when the primary current passes from negative to positive values for the directions of transformer excitation assumed in Fig. 2, the pulse transmission being suppressed when the current to be interrupted passes from positive to negative values.

if the switch to be controlled is to be opened at a given moment in response to a manual control action or in response to an overload current, it is also necessary to connect into the circuit of control coil 2 a device which permits the releasing pulse to become effective only at the desired moment. For instance, an overload relay may be provided whose coil is series connected with winding. 4 and whose normally open contact is series connected with coil 2.. When the relay responds to overload in the primary circuit, its contact closes and a pulse is thereafter transmitted to the coil 2 at the next zero passage of the primary current at which this current changes from negative to positive values. However, the release control apparatus may also be used when the switch is to be opened and closed periodically as is the case, for instance, when the switch forms part of a contact converter. The switch is then equipped with a second control winding which causes the switch to close and is energized by control pulses at the correct moment. An embodiment of this kind will be described in a later place with reference to Fig. 6.

While in the apparatus according to Fig. 1, the constant excitation of the saturable pulsing transformer is produced by an additional winding 6, it is also possible to use a permanent magnet for this purpose. An embodiment of the latter kind is illustrated in Fig. 5, the same reference numbers being used as in Fig. l for denoting respectively similar elements.

The core of the pulsing transformer 3 in the embodiment of Fig. 5 has an air gap 15 so dimensioned that it does not unduly affect the characteristic of the transformer. Arranged in magnetic parallel relation to gap 15 is a permanent magnet 16. The flux of this magnet passes mainly through the air gap 15. However, part of this flux passes through the core portion which carries the windings of the saturable transformer and produces the desired constant premagnetization. The air gap is needed for preventing the alternating flux caused by the alternating current excitation of the transformer from reversely magnetizing the permanent magnet 16. A shunt (not illustrated) across the permanent magnet may be added for adapting the permanent flux through the main portion of the transformer core to the above-explained conditions.

In the foregoing explanation of the operation, it was assumed that the saturation characteristic of the pulsing transformer is rectangular. This, however, is not an essential requirement, it being only necessary that the knee or bend of the magnetization curve is well pronounced. For instance, in the embodiment according to Fig. 5 a rectangular magnetization characteristic is hardly obtainable due to the presence of the air gap. The magnetic characteristic of such an air-gap transformer extends essentially in a somewhat slanted direction to the abscissa in the unsaturated range and is horizontal in the saturated range.

The above-mentioned use of apparatus according to the invention as part of a contact converter will be more fully understood from the embodiment of a three-phase contact rectifier illustrated in Fig. 6. The rectifier is energized from its line terminals through a power transformer T whose secondary windings U, V and W produce three mutually phase-displaced voltages which are rectified by three synchronous contact devices C (only one shown) to energize a direct-current load L.

Series-connected in each phase circuit of respective transformer secondaries U, V, and W is a saturable switching reactor S of the kind previously mentioned. This reactor is saturated most of the time but becomes temporarily unsaturated when the phase current passes through the zero value. As a result the reactor abruptly increases its reactance near the current zero passages, thus reducing the current amplitude and providing a flattened current step within which the switch contact 1 may open without sparking. Each switching reactor may be equipped with premagnetizing circuits which are not shown and need not be described as they are well known and not essential to the invention proper.

In the following reference is made mainly to the more fully illustrated details of the phase circuit pertaining to the transformer winding U. It will be understood, that the two other phase circuits are equipped and operative in the same way except that the pertaining switches operate in phase displaced relation to that of the phase circuit for winding U.

As shown in Fig. 6, the contact member 1 consists essentially of a ferromagnetic armature which is elastically suspended by spring wires. The armature may have its underside coated with an electrically good conducting material. The operation of the contact device C is controlled by two composite magnet structures 21 and 22. Each magnet structure comprises a magnetic circuit whose pole shoes face the armature member 1, a permanent magnet 23 or 24, and an air gap 24a in magnetic parallel relation to each of the pole shoes. Magnet structure 22 (break control magnet) carries the abovementioned release winding 2. Magnet structure 21 (make control magnet) has a similar winding 25. Winding 25 is excited from the secondary winding 26 of a saturable transformer 27 whose primary winding 28 is series connected with an ohmic resistor 29 and a choke coil 30 across the transformer winding U. The saturable transformer 27, which as shown may have a toroidal core, is unsaturated at Zero current but operates within its range of saturation as soon as the primary current assumes a slight instantaneous value. Consequently, a sharp pulse is induced in the secondary winding 26. This pulse is applied to the winding 25 of the switching-on magnet 21. By suitably dimensioning the circuit resistances, these pulses can be made to occur at the correct moments.

The winding 2 of break control magnet 22 is connected with the secondary Winding 7 of the saturable transformer 3 whose primary winding 4 is series connected with the switching reactor S. The transformer 3 and its circuit connections are the same as the corresponding elements shown in Fig. 1 and described previously, the reference numerals 1 to 12 in Fig. 6 denoting the same respective elements as in Fig. 1.

When the winding 2 on break control magnet 22 receives a pulse, it induces in the magnetic circuit a flux opposed to that of the permanent magnet 24. Consequently, the magnetic holding force of magnet 22 is suddenly reduced so that the biasing suspension springs swing the armature to the open position. Due to its momentum, the armature moves beyond the zero bias position into the effective field range of the magnet 21 which then retains the armature 1. When thereafter the winding 25 of make control magnet 21 receives a pulse, the flux passing from the permanent magnet 23 through the armature 1 is weakened so that the biasing springs become again eifective to move the armature 1 toward the other holding magnet 22 where the armature 1 is again caught by the magnet field.

In all other respects the release control device of the contact rectifier of Fig. 6 operates in the same manner as explained in the foregoing with reference to Fig. 1.

It will be understood by those skilled in the art that the invention permits of various modifications other than those specifically shown and described, without departing from the objects and features of the invention and within the scope of the claims annexed hereto.

I claim:

1. In combination, an alternating current main circuit to be controlled, a contact device having contact means connected in said main circuit and having a pulse-responsive release circuit operative to control said contact means to open said main circuit upon receiving a current pulse of a given magnitude, a saturable-core transformer having a first primary winding series connected with said contact means in said main circuit, a second primary Winding on said transformer, an inductance connected in series in said main circuit, circuit means including said inductance for energizing said second primary winding with a leading current, said transformer having additional constant excitation means and having a secondary Winding connected with said release circuit for issuing pulses thereto, said constant excitation means producing in said transformer an ampere turn magnitude substantially equal to that required to produce in said secondary winding a current equal to said current pulse of given magnitude.

2. In combination, an alternating-current main circuit to be controlled, a contact device having contact means connected in said main circuit and having a pulse-responsive release circuit operative to control said contact means to open said main circuit upon the pulse reaching a given amplitude, 21 saturable-core transformer having constant premagnetizing means and having three windings, one of said windings being series connected with said contact means in said main circuit, an inductance connected in said main circuit and having a voltage proportional to the rate of change of the alternating current in said main circuit, a resistor, said inductance being connected through said resistor to another one of said windings for exciting said latter winding by said voltage, and said third winding being connected with said release circuit for initiating therein a releasing pulse at a given moment prior to the zero passage of said main circuit current, said premagnetizing means producing in said transformer an ampere turn magnitude substantially equal to that required to produce in said third winding a current equal to said current pulse of given magnitude.

3. In combination, an alternating-current main circuit to be controlled, at contact device having contact means connected in said main circuit and having a pulse-responsive release circuit for controlling said contact means to open said main circuit upon passage of a current pulse of given magnitude through said circuit, a saturable-core transformer having four windings of which one is series connected with said contact means in said main circuit, a reactive impedance member connected in said main circuit and having a voltage substantially proportional to the rate of change of the alternating current in said main circuit, a resistor, said member being connected through said resistor to a second one of said windings, and a direc current bias circuit of constant voltage connected with a third one of said windings for constantly premagnetizing said transformer, the fourth Winding of said transformer being connected with said release circuit for initiating therein a releasing pulse at a given moment prior to the zero passage of said main circuit current. said premagnetizing bias circuit producing in said third Winding an ampere turn magnitude substantially equal to that re quired to produce in said fourth winding a current equal to said current pulse of given magnitude.

4. In combination, an alternating-current main circuit to be controlled, a contact device having contact means series connected in said main circuit and having a release circuit responsive to a current of given magnitude to control said contact means so as to open said main circuit,

a saturable-core transformer having a winding series connected with said contact means in said main circuit and having excitation means responsive to the differential quotient of the alternating current in said main circuit, a secondary Winding on said transformer connected with said release circuit for initiating therein a releasing pulse at a given moment prior to the zero passage of said current, said transformer having constant premagnetizing means of an ampere turn magnitude equal to that required for producing in said secondary winding a current substantially equal to said current of given magnitude.

5. In a combination according to claim'l, said constant excitation means comprising a permanent magnet, and said saturable-core transformer having a magnetizable core joined with said magnet to receive constant magnetic flux from said magnet.

References Cited in the file of this patent UNITED STATES PATENTS 1,671,471 Fortescue May 29, 1928 1,787,931 Besold Ian. 6, 1931 2,283,697 Prince May 19, 1942 2,499,394 Kesselring Mar. 7, 1950 Kesselring Nov. 25, 1952 

